A high-throughput method for viscosity measurement was developed and tested for nanocomposite sols with an easy-to-clean (ETC) effect. The method is based on doping of sols with viscosity sensitive fluorescent dye 4,4'-bis-(2-benzoxazolyl)-stilbene (BOS) and acquisition of fluorescence intensity data. The spectroscopic data were correlated with viscosity data derived from mechanical measurements with a rotational viscometer and show an exponential correlation of both mechanical and spectroscopic measurement methods in the relevant data space of 3-5 mPa center dot s. For application of the spectroscopic viscosity measurement as a high-throughput assay doping of sols with BOS slurry was carried out with an automated liquid handling system, and spectroscopic measurements were performed with a fluorescence microplate reader.